1. Field of the Invention
The present invention relates to a complementary metal-oxide-semiconductor (CMOS) integrated circuit and an amplifying circuit.
2. Description of the Related Art
In a wireless communications system such as a mobile phone or a wireless data communications device, an amplifying circuit for amplifying a received signal is installed on a signal-receiving side. A low noise amplifier (LNA) may be provided as an example of an amplifying circuit. The LNA amplifies a signal while reducing noise generated in the circuit itself by as much as possible, and is an essential circuit disposed at a front end of a wireless signal receiving circuit.
An LNA implemented with a complementary metal-oxide-semiconductor (CMOS) is increasingly in demand so as to lower the price of the LNA. Further, the reduction in a noise factor (NF) and the implementation of a high degree of linearity, capable of removing interference waves, are always required, due to the original role of the LNA.
In addition, a silicon on insulator (SOI) substrate is frequently used when the LNA is implemented with a CMOS (please see the Related Art Document). The SOI substrate is suitable for an LNA circuit, since an inductor or a transistor having a high Q value due to the high resistance of a substrate has relatively low parasitic resistance. In addition, a so-called floating body type MOS transistor in which a body potential is not fixed due to a low parasitic capacitance is frequently used as the input transistor of the CMOS LAN using the SOI substrate.
However, it is difficult to achieve a high degree of linearity in the floating body type metal-oxide-semiconductor (MOS) transistor, due to a kink phenomenon, peculiar to a silicon on insulator (SOI) substrate. The kink phenomenon is a non-linearity phenomenon of current over drain voltage. Therefore, in order to improve low noise amplifier (LNA) performance, it is necessary to avoid this non-linearity phenomenon when an LNA circuit is formed on the SOI substrate. Even in the case that the LNA circuit is formed by using a bulk CMOS process, it is also required to avoid deterioration of NF characteristic and achieve a high degree of linearity.